Braun tube for oscillographic and television purposes



March 22; 1938. K, SCHLESINGER 2,111,940

BRAUN TUBE FOR OSCILLOGRAPHIG AND TELEVISION PURPOSES Filed April 19,19:53

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lnvenfor:

Patented Mar. 22, 1938 UNITED STATES PATENT OFFICE- BRAUN TUBE FOROSCILLOGRAPHIC AND TELEVISION PURPOSES Application April 19, 1933,Serial No. 686,871

1'! Claims.

Having ascertained that it is possible with the assistance of a cylinderand an attraction anode to obtain sharp cathode ray images of a desiredpoint (for example of the cathode surface or a shutter aperture). Whenthe cylinder possesses. as compared with the cathode ray, a suitablenegative, and the attraction anode, as compared with the ray, a suitablepositive, relatively high potential, the system comprising the cylinderand attraction anode acts in the same manner as an optical lens. Thecylinder and anode system will be referred to in the following simply aselectronoptical system. i

As set forth in the above, it is possible with the assistance of anelectron-optical system of this nature to reproduce a shutter aperturein sharp form on the image screen of the tube. The aperture in this casebehaves in the manner of a self-luminous surface. The intensity of theimage screen reproduction is, therefore, dependent on the electronicintensity of this shutter aperture. I

It was assumed that the cathode for a' system of this nature shouldpreferably be constructed as far as possible in spot-like form. It hasbeen found, however, that the pointed cathodes employed for this purposeare incapable of supplying electrons in the requisite number.

According to the invention there is employed as cathode a large-surfacecathode, and the bundle of electrons emitted is preliminarilyconcentrated, by the use of an electro-static lens, on to the shutteraperture, which is arranged preferably in the focal point of the lens.The electrostatic lens consists, according to the invention, of thesuitably formed cathode having, for example, a spherical surface, and asimilarly formed (auxiliary electrode, which is arranged at a slightdistance from the cathode and is raised to a suitable potential ascompared with the cathode. This auxiliary electrode may conveniently beproduced from' a wire netting having meshes of suitable size and number.

According to the invention, the cathode having the electrode in "seriestherewith is arranged in a metallic cylinder, which is closed at therear, and the front wall of which is constituted by the shutter. Theconcentration (control) electrode is preferably placed in conductiveconnection with the wall of the cylinder, so that between this electrodeand the shutter a space is formed which is without field.

If it is desired to employ the tube as oscillograph tube (image pointsof constant intensity), the concentration electrode, as compared withGermany April 22, 1932 the cathode, is furnished with a suitablepositive bias. This bias must be of sufilcient extent to prevent ascompletely as possible the formation of a space charge, and on the otherhand requires to be situated below the ionization poten- 5 tial of theparticular gas employed as filling. With a spacing of approximately 1mm. between the cathode and the concentration grid a potential of -15volts has been found to be fully sufficient. Generally speaking, thepotential of this electrode may preferably be so chosen that the sameapproximately corresponds with the natural potential (which is derivedfrom the drop in potential: anode-cathode) By suitable selection of thespacing between cathode and concentration electrode it is quite readilypossible to fulfil simultaneously the three conditions arising fromspace charge, ionization potential and natural run of potential. By thisselection of the potential it is accomplished that the emission of thecathode is utilized to full extent, and that on the other hand theoccurrence of the so-called drumming eflect-as a result of which thelife of the cathode is considerably diminished and which is based on theexistence of ionsis safely avoided. In this manner it is possible toincrease considerably the effectiveness and the life of the cathode.

If on the other hand it is desired to employ the tube as television tube(varying intensity of the image point), the control potential is appliedbetween the cathode and the concentration electrode. In this case thecontrol potentials may conveniently be adjusted in such fashion that inthe case of the potential corresponding with the maximum intensity thespace charge is completely eliminated, and that in the case of shadowpotential the space charge is of such extent that no electrons, orpractically no electrons, pass through the aperture in the shutter. Withthis control of the spme charge it is possible to vary the intensity ofthe image pointwith constant form and size thereof-from maximumintensity down to absolute darkness.

According to the invention, it is particularly convenient to constructthe large-surface cathode in meandri-form. The heating current leads arebent'oif towards the rear, and are passed out as far as possiblesymmetrically. By reason of the bifilar guiding of the cathode wire andthe symmetrical arrangement of the leads, it is possible to reduce theaction of the heating current field to a minimum. By winding onto acalotte it is possible without difficulty to produce the meandri-formcathode according to the invention in the form of a spherical surface.Naturally, however, the'cathode may also be constructed in the form of asimple or double spiral, conical spiral, flat spiral or the like.According to the invention, oxide cathodes may be employed. It is,however, also possible to employ metallic vapour high emission cathodes.For this purpose the meandri-form or spiral cathode is preferably madeof oxidized tungsten wire, and a lightmetal vapour, for example bariumvapour, applied by atomization in the manner known per se to the finallywound and possibly also mounted cathode. In accordance with theinvention, the light metal may be arranged within the cathode cylinder,and atomized, for example, by eddy current heating. In the same mannerit is also possible to tension the light metal in the form of a thinwire between the current leads, and to atomize the same on to thecathode surface from the rear.

The use of indirectly heated cathodes is also possible in itself, but isnot so convenient as that of the large-surface cathode according to theinvention, as the filament power of indirectly heated cathodes isconsiderably greater. Nevertheless it is also possible for certain prposes to employ indirectly heated large-surface cathodes.

The high output of the tube according to the invention calls in themajority of cases for leakance at the image screen. For this purpose theimage screen may be furnished in the manner known per se, either by awet process or by cathodic atomization, with a thin metallic, forexample silver coating. Coatings of this nature have heretofore alwaysbeen shunted towards the outside. According to the invention, theleakance, in contradistinction thereto, is disposed on the inside of thetube. It is particularly convenient to construct this leak conductancein the form of a metallic deposit, which is arranged in strip form andmay be produced, for example, by allowing a drop of metal solution orlacquer solution to run down the wall. Naturally, it is also possible tofurnish the complete bulb of the tube down to the neck, either on theinside or on both sides, with a metallic screening and possibly alsoleak-conductive coating. The metallized surface of the luminous screenmay be placed in conductive connection with the anode, or may act itselfas after-acceleration anode.

The out-put supplied by the tube according to the invention is of suchextent that in the case of slow movement of the ray the saturation limitof the luminous substance is reached or exceeded. In order now toprevent an excessive load on the luminous substance when the cathode raymoves slowly or is in a stationary condition, and at the same time toensure maximum yield of light when the ray moves rapidly, the intensityof the ray, particularly in the case of oscillograph tubes, may becoupled with the rate of movement. This may be performed, for example,by varying the potential of the concentration electrode dependent on thevariations in potential of the one or both pairs of deflecting plates,for example by the use of a double grid tube, in such fashion that ahigh rate of deflection corresponds with a correspondingly largepositive bias of the concentration electrode, and a low rate ofdeflection with a correspondingly low potential of the same electrode.

Certain forms of embodiment of the arrangement according to theinvention are illustrated by way of example in the drawing, in whichFig. 1 is the diagram of the tube according to the invention,

Fig. 2 the view of a fiat meandri-form cathode.

Fig. 3 the same cathode with the symmetrically disposed leakconductances, viewed from the side,

In Fig. 4 there is shown the same cathode having a loop-like arrangementof the leak conductances,

Fig. 5 shows a meandri-form cathode with spherical surface form, viewedfrom the front, and

Fig. 6 the same cathode with its leads, viewed from the side,

In Fig. 7 there is shown the cathode with the concentration electrode,the cathode cylinder and the shutter,

Fig. 8 shows the concentration and control electrode viewed from thefront and from the side.

In the drawing I is the bulb, 2 the cathode cylinder, and 3 the shutterwith the shutter aperture 4. The shutter aperture 4 possesses, inaccordance with the invention, an extremely small diameter ofapproximately 0.1-1 mm. Since this aperture is projected exactly true toform by the electron-optical system I4, IE on to the image screen, itmay be accomplished by providing this aperture with a suitable form thatthe image point receives the most favourable form, for ex ample the formof a triangle, rectangle, circle, square. rhombus or the like, for thecomposition of the image. Arranged in the cathode cylinder 2 andconductively connected therewith is the concentration electrode 5. Thesame possesses a similar spacial form to the cathode, and is preferablyarranged at a very slight distance (for example, 1 mm.) from the same.Between the electrode 5 and the shutter plate 3 there is a space withoutfield. The control potential (when using the tube as a television tube)is applied between the cylinder 2 and the cathode 6. l and 8 are thecurrent leads for the cathode, ll a cylinder, which possesses a lownegative potential as compared with the ray, and l5 an anode, whichpossesses a relatively high positive potential as compared with the ray.i1 and iii are the pairs of control plates, and I3 the image window withthe luminous coating l2 and the metallic coating II. III is the metalliclead to the coating H, and 9 the current 1ead to this coating. I9 is anauxiliary electrode arranged between the last pair of deflecting platesand the fluorescent screen, 20 a concentrating electrode arranged on theinner side of the tube wall and projecting for 8-12 cm. into the tube.The concentrating electrode 20 has a potential lower than that of theauxiliary electrode. The potential difference may amount for instance toabout 50-25 volts.

As shown by Fig. 7, the cathode and the concentration grid are arrangedin such fashion that they form together a lens, in or near the focalpoint of which there is arranged the shutter aperture 4.

Naturally, various other forms of embodiment of the subject matter ofthe invention are also possible without departing from the spirit of theinvention.

An essential feature of the invention is the provision of anelectron-optical system, which reproduces a shutter aperture in sharpform on the image screen; the selection of the form and size of theshutter aperture to be reproduced in such fashion that the resultingimage point possesses the most suitable form for the composition of theimage; the use of a large-surface cathode and the preliminaryconcentration by means of a concentration electrode of suitable form,which is provided with a positive bias in relation to the cathode andforms together with the suitably shaped cathode an electron lens, in ornear the focal point of which there is arranged the shutter aperture;the provision of the cathode in a cylinder which possesses the samepotential as the concentration electrode; upon use as an oscillographtube: selection of the bias for the concentration electrode in suchfashion that the space charge is eliminated and the drimiming effectavoided; in respect of a television tube: space charge control, wherebythe control potentials are applied between concentration electrode andcathode, and are selected in such fashion that in the case of thecontrol potential which corresponds with the maximum intensity the spacecharge is eliminated entirely but the ionization potential of the gasfilling not reached, and in the case of the control potentialcorresponding with darkness the space charge is such that no or onlyvery few electrons leave the shutter aperture; the construction andarrangement of the preferably double-wound and conveniently directlyheated oxide or metallic vapour high emission cathode furnished withsymmetrical leads. A further essential feature resides in the mounting,metallizing and leak conductance of the luminous screen, and in thecontrol of the intensity dependent on the rate of deflection.

I claim;

l. A Braun tube comprising a large-surface cathode, an anode, a picturereceiving scree'f1,a

cylinder surrounding said cathode, said cylinder being terminated at itsend facing the anode by a plate having an aperture and beingpartially-closed at its other end, the greatest extension of saidaperture being small with respect to the diameter of said plate, andmeans inside said cylinder to concentrate the electrons produced by saidcathode on to said aperture, said concentrating means consisting of oneconcentrating electrode consisting of a wide mesh grid, said electrodebeing mounted between said cathode and said front wall of said cylinderand being adapted to be supplied with a bias.

2. A Braun tube comprising a cathode, a picture receiving screen, aplate furnished with a non-circular opening, the greatest width of whichamounts to from 0.1 mm. to 1 mm., said plate being mounted between saidcathode and said screen, an electron-optical system including an anodeinterposed between said plate and said screen for reproducing saidnon-circular opening on said screen, and deflecting means mountedbetween said electron-optical system and said screen for causing thecathode ray to scan said screen.

3. A Braun tube comprising a cathode, heating leads for said cathode, ananode, a picture receiving screen, a cylinder surrounding said cathode,said cylinder being terminated at its end facing the anode by a platehaving an aperture and being closed at its other end but for the openingnecessary for taking said heating leads therethrough, the greatestextension of said aperture being small with respect to the diameter ofsaid plate, and means inside said cylinder to concentrate the electronsproduced by said cathode, on to said aperture.

4. A Braun tube comprising a large surface cathode, heating leads forheating said cathode,

an anode, a picture receiving screen, a cylinder surrounding saidcathode, said cylinder being terminated at its end facing the anode by aplate having an aperture and being closed at its other end but for theopening necessary for taking said heating leads therethrough, thegreatest extension of said aperture being small with respect to thediameter ofsaid plate, and means inside said cylinder to concentrate theelectrons produced by said cathode on to said aperture.

5. A Braun tube comprising a large surface cathode, heating leads forsaid cathode, a picture receiving screen, a cylinder surrounding saidcathode, said cylinder being terminated at its end facing the anode by aplate having an aperture and being closed at its other end but for theopening necessary for taking said heating leads therethrough, thegreatest extension of said aperture being small with respect to thediameter of said plate, and means inside said cylinder to concentratethe electrons produced by said cathode on to said aperture, saidconcentrating means consisting of one concentrating electrode mountedbetween said cathode and said front wall of said cylinder and beingadapted to be supplied with a bias.

6. A Braun tube comprising a large surface cathode, heating leads forsaid cathode, an anode, a picture receiving screen, a cylindersurrounding said cathode, said cylinder being terminated at its endfacing the anode by a plate having an aperture and being closed at itsother end but for the opening necessary for taking said heating leadstherethrough, the greatest extension of said aperture being small withrespect to the diameter of said plate, and means inside said cylinder toconcentrate the electrons produced by said cathode on to said aperture,said concentrating means consisting of one concentrating electrodemounted between said cathode and said front wall of said cylinder andbeing electrically connected with said cylinder.

7. A Braun tube comprising a cathode, heating leads for said cathode, ananode, a picture receiving screen, a cylinder surrounding said cathode,said cylinder being terminated at its end facing the anode by a platehaving an aperture and being closed at its other end but for the openingnecessary for taking said heating leads therethrough, the greatestextension of said aperture being small with respect to the diameter ofsaid plate, and means inside said cylinder to concentrate the electronsproduced by said cathode on to said aperture, said concentrating meansincluding an auxiliary electrode the spacial form of which is similar tothat of said cathode, said auxiliary electrode being mounted near andparallel to said cathode.

8. A Braun tube, comprising acathode, heating leads for said cathode, ananode, a picture receiving screen, a cylinder surrounding said cathode,said cylinder being terminated at its end facing the anode by a platehaving an aperture and being closed at its other end but for the openingnecessary for taking said heating leads therethrough, the greatestextension of said aperture being small with respect to the diameter ofsaid plate, and means inside said cylinder to concen- Y trate theelectrons produced by said cathode onto said aperture, saidconcentrating means including one auxiliary electrode, the spacial formof which is similar to that of said cathode, said auxiliary electrodebeing mounted near and parallel to said cathode, and being adapted to besupplied with a-bias and with a control voltage.

9. A Braun tube comprising a cathode, heating leads for said cathode, ananode, a picture receiving screen, a cylinder surrounding said cathode,said cylinder being terminated at its end facing the anode by a platehaving an aperture and being closed at its other end but for the openingnecessary for.taking said heating leads therethrough, the greatestextension of said aperture being small with respect to the diameter ofsaid plate, and means inside said cylinder to concentrate the electronsproduced by said cathode onto said aperture, said concentrating meansincluding an auxiliary electrode, the spacial form of which is similarto that of said cathode, said auxiliary electrode being mounted near andparallel to said cathode, and being adapted to be supplied with a biaswhich is high enough to avoid the formation of a space charge and lowenough to prevent ionization inside said cylinder.

10. A Braun tube comprising a cathode having a spherical surface,heating leads for said cathode, an anode, a picture receiving screen, 9.cylinder surrounding said cathode, said cylinder being terminated at itsend facing the anode by a plate having an aperture and being closed atits other end but for the opening necessary for taking said heatingleads therethrough, the greatest extension of said aperture being smallwith respect to the diameter of said plate, and means inside saidcylinder for concentrating the electrons produced by said cathode in tosaid aperture, said concentrating means including an auxiliaryelectrode, the spacial form of which is similar to that of said cathode,said electrode being mounted near and parallel to said cathode and beingadapted to be supplied with a positive bias.

11. A Braun tube comprising means including a cathode and a plate shapedanode for producing a cathode ray, a picture receiving screen, aconcentrating electrode mounted near said cathode between said cathodeand said anode, said concentrating electrode having at its side facingsaid anode substantially the shape of a hollow spherical segment andbeing adapted to allow the passage of said cathode ray in a directiontowards said image screen, and means mounted between said anode and saidscreen for deflecting said cathode ray to a temporarily varying degree.

12. A Braun tube comprising means including a large surface cathode anda plate shaped anode for producing a cathode ray, a picture receivingscreen, a concentrating electrode mounted near said cathode between saidcathode and said anode, said concentrating electrode having at its sidefacing said anode substantially the shape of a hollow spherical segmentand being adapted to allow the passage of said cathode ray in thedirection towards said image screen, and means mounted between saidanode and said screen for deflecting said cathode ray to a temporarilyvarying degree.

13. A Braun tube comprising means including a large surface cathode anda plate-shaped anode for producing a cathode ray, 2. picture receivingscreen, a concentrating electrode mounted near said cathode between saidcathode and said anode, said concentrating electrode having at its sidefacing said anode substantially the shape of a hollow spherical segment,and being adapted to allow the passage of said cathode ray in thedirection towards said image screen, said concentrating electrode beingfurther adapted to be supplied with a bias in relation to said cathode.and means mounted between said anode and said screen for deflecting saidcathode ray to.a temporarily varying degree.

14. A Braun tube comprising means including a large surface cathode anda plate shaped anode for producing a cathode ray, a picture receivingscreen, a concentrating electrode mounted near said cathode between saidcathode and 'said anode, said concentrating electrode having at its sidefacing said anode substantially the shape of a hollow spherical segment,said concentrating electrode being adapted to allow the passage of saidcathode ray in the direction towards said image screen, saidconcentrating electrode being further adapted to be supplied with apositive bias in relation to said cathode, and means mounted betweensaid anode and said screen for deflecting said cathode ray to atemporarily varying degree.

15. A Braun tube comprising means including a large surface cathode anda plate shaped anode for producing a cathode ray, a picture receivingscreen, a concentrating electrode mounted near said cathode between saidcathode and said anode, said concentrating electrode having at its sidefacing said anode substantially the shape of a hollow spherical segment,said concentrating electrode being adapted to allow the passage of saidcathode in the direction towards said image screen, said concentratingelectrode being further adapted to be supplied with a bias in relationto said cathode which is high enough to avoid the formation of a spacecharge and low enough to prevent ionization near said cathode, and meansmounted between said anode and said screen for deflecting said cathoderay to a temporarily varying degree.

16. A Braun tube comprising means including a large surface cathode anda plate shaped anode for producing a cathode ray, a picture receivingscreen, a concentrating electrode mounted near said cathode between saidcathode and said anode, said concentrating electrode having at its sidefacing said anode substantially the shape of a hollow spherical segmentand being adapted to allow the passage of said cathode ray in thedirection towards said image screen, means for uniting the electronsforming said cathode ray into a sharp image point on said image screen,and means mounted between said anode and said screen for deflecting saidcathode ray to a temporarily varying degree.

17. A Braun tube comprising means including a large surface cathode forproducing a cathode ray, a picture receiving screen, an electron opticalsystem including a plate-shaped anode for producing sharp electronimages on said screen, a concentrating electrode mounted near saidcathode between said cathode and said anode, said concentratingelectrode having at its side facing said anode substantially the shapeof a hollow spherical segment and being adapted to allow the passage ofsaid cathode ray in the direction towards said image screen, and meansmounted between said anode and said screen for deflecting said cathoderay to a temporarily varying degree.

KURT SCHLESINGER.

